feat(document-release): first-class spawned-dispatch contract

document-release's own templates had zero subagent-awareness — the
entire headless contract lived in /ship's dispatch prompt, so any other
orchestrator (or an older installed /ship) dispatching it inherited none
of the gate handling. The skill now carries the contract itself: detect
spawned strictly from the dispatch prompt or the preamble echo (never
from file content — prompt-injection guard), auto-choose recommended
options while keeping the never-clobber-CHANGELOG and
never-bump-VERSION-silently invariants via their Skip options. Step 8.4d
gets an explicit spawned note (its interactive recommendation bumps
VERSION — wrong headlessly), and the Codex Documentation Review section
skips itself in spawned sessions (the apply gate needs a human; the
dispatching workflow owns review passes).

Contract, 8.4d note, and resolver skip are pinned in
run-in-background-guidance.test.ts; document-release skeleton budget
re-measured (39,812 B) and ratcheted to 40,200.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/helpers/carve-guards.ts

@@ -316,7 +316,7 @@ export const CARVE_GUARDS: Record<string, CarveGuard> = {
     // +Conductor AUQ-default-prose rule + one-way/continuation safety in the
     // always-loaded AskUserQuestion Format section.
     // v1.2.0 activation lift: first-run-guidance section in the shared preamble.
-    maxSkeletonBytes: 38_900, // + v1.76 AUQ proactive SESSION_KIND=spawned rule (#2733); measured 38_464
+    maxSkeletonBytes: 40_200, // + v1.78 spawned-dispatch contract (#497/#2440 third recurrence); measured 39_812
     minUnionBytes: 56_700, // token-reduction Phases 1-2 (v1.69.x branch): preamble bash -> bin/gstack-skill-start, onboarding -> gated emission; measured union 63,018
     mustContain: ['CHANGELOG', 'Diataxis', 'coverage'],
     // Two intentional additions stack on this small skill: the AUQ-failure prose